James C. Lombardi

Evolution of stellar collision products in globular clusters. I. Head-on collisions

We explore the evolution of collisionally merged stars in the blue straggler region of the H-R diagram. The starting models for our stellar evolution calculations are the results of the smoothed particle hydrodynamics (SPH) simulations of parabolic collisions between main-sequence stars performed by Lombardi, Rasio, & Shapiro. Since SPH and stellar evolution codes employ different and often contradictory approximations, it is necessary to treat the evolution of these products carefully. The mixture and disparity of the relevant timescales (hydrodynamic, thermal relaxation, and nuclear burning) and of the important physical assumptions between the codes makes the combined analysis of the problem challenging, especially during the initial thermal relaxation of the star. In particular, the treatment of convection is important and semiconvection must be modeled in some detail. The products of seven head-on collisions are evolved through their initial thermal relaxation and then through the main-sequence phase to the base of the giant branch. Their evolutionary tracks are presented. In contrast to what was assumed in previous work, these collision products do not develop substantial convective regions during their thermal relaxation and therefore are not mixed significantly after the collision.

Collisions of main-sequence stars and the formation of blue stragglers in globular clusters

We report the results of new SPH calculations of parabolic collisions between two main-sequence stars in a globular cluster. Such collisions are directly relevant to the formation of blue stragglers. In particular, we consider parent stars of mass

On blue straggler formation by direct collisions of main sequence stars

M/M_{TO}=0.2,0.5,0.75

V1309 Sco—UNDERSTANDING A MERGER

, and

Identification of the Long-Sought Common-Envelope Events

1

Tests of Spurious Transport in Smoothed Particle Hydrodynamics

, where

FORMATION OF BLACK HOLE X-RAY BINARIES IN GLOBULAR CLUSTERS

M_{TO}

Tidal Breakup of Binary Stars at the Galactic Center. II. Hydrodynamic Simulations

is the cluster turnoff mass (typically about

On the onset of runaway stellar collisions in dense star clusters - II. Hydrodynamics of three-body interactions

0.8\,M_\odot

Recombination energy in double white dwarf formation

). Low-mass stars (with